reusing lighting circuits with shared neutral

malachi constant

Senior Member
Location
Minneapolis
Hi all,
I'm a specifying engineer. An Owner expressed concerns about an upcoming lighting upgrades project where new commercial grade LED troffers (think Acuity BLT or equivalent) will replace existing fluorescents one-for-one. Their concern is the wiring, while in good condition, utilizes shared neutrals. They own many properties and believe some time, some where, they experienced flickering with new LED fixtures that were installed on circuits with shared neutrals. They don't have the specifics so impossible to investigate. If we have to rewire the branch circuits the project will potentially die due to budget issues - the Owner will defer to my "engineering judgement" so want to collect as much info as possible. I've been specifying LED since troffers hit the market in force about 6 years ago and we've reused a lot of circuits with shared neutrals. I am not aware of this being an issue, nor are the lighting reps I have contacted. Figured I would ask the community here if you have any history with this situation.
Thanks and have a great weekend!
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Just my opinion but the fixtures should work just fine on a MWBC unless for some reason the manufacturer specifies using only 2-wire circuits.
 

malachi constant

Senior Member
Location
Minneapolis
Is the switching such that you need all the branch circuits? How much are you reducing the load. Can you get by with one vs three?
That's an interesting approach. The LED would be pretty close to a third the fluorescent wattage. If we proceed reusing the circuitry I'll put that in my back pocket in case things go sideways.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Someone should say it: the owner just has no idea what they're talking about.

I mean, it's certainly possible they had flickering on circuits with shared neutrals, but almost impossible it was *because of* the shared neutrals.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
There is no way you will not use shared neutral.

The individual branch circuit might not have a shared neutral, but the panel feeder is virtually certain to have a shared neutral.

While I could imagine a fixture that was sensitive to interference somehow stronger on a shared neutral branch circuit (say some sort of sensitivity to 3rd harmonic caused by the fixtures themselves) I would call that a defective fixture and not a problem with the shared neutral.

Jon
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
Does the owner have a backup generator? Miswiring of circuits with an SDS generator can cause issues if the generator neutral wasn’t properly bonded, and the wrong neutral is used with the circuit. This usually ends up frying a bunch of drivers. Other than that, no problem using shared neutrals. Another manufacturer (not Accuity) thought they would be smart, and build in a transferswitch into their fixtures. Problem was, the engineer that designed it was switching only the hots, not the neutrals. The neutral on the SDS generator was not bonded, causing a good chunk of the fixtures to go “open neutral”. Along with illegally using the normal source neutral with the emergency source hot. That manufacturer is changing thousands of fixtures out at their own expense, along with the customer having their generator wiring checked.
 

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
Someone should say it: the owner just has no idea what they're talking about.

I mean, it's certainly possible they had flickering on circuits with shared neutrals, but almost impossible it was *because of* the shared neutrals.
Probably had an electrician who had no way to idea, and simply blamed it on neutral issue
 

malachi constant

Senior Member
Location
Minneapolis
Hi all - thank you for the input here.
I reached out to three lighting vendors and they in turn reached out to their major manufacturers - no one at any level is aware of shared neutrals causing an issue with flickering.
I think the Owner was fed some bad information from someone in the distant past.
 
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